There is no one clear-cut sign that identifies pyoderma gangrenosum. Although the appearance of the ulcer (purple edges) is distinctive, many diseases cause ulcers resembling pyoderma gangrenosum. In fact, pyoderma gangrenosum is often misdiagnosed.
Mayo researchers reviewed several hundred cases diagnosed as pyoderma gangrenosum at Mayo and other centers. It found that two-thirds of people were initially misdiagnosed as having another disease and received the wrong treatment. Half the time, the treatment they received was either of no help or was harmful. So getting the right diagnosis is crucial.
In general, Mayo takes a four-step approach to this disease.
- A thorough examination by a dermatologist to understand what is going on.
- Biopsy of the ulcer. In Mayo's study, a biopsy identified an alternative cause of the ulcer in more than half the cases.
- Lab tests. No lab test identifies pyoderma gangrenosum. But testing can identify other causes of the ulcer.
- If pyoderma gangrenosum does not respond to the standard therapy, the diagnosis should be reconsidered and other possible causes explored.
Tests frequently used in diagnosis of pyoderma gangrenosum include:
- Routine blood tests, including a complete blood count; a comprehensive chemistry profile, including a liver function test and urinalysis
- A hepatitis profile to rule out hepatitis
- Tests for diseases of white or red blood cells
- Cultures for bacteria, fungi, atypical mycobacteria and viruses
- A colonoscopy or other tests to exclude inflammatory bowel disease or ulcerative colitis
- Angiography or Doppler echocardiography when arterial or venous insufficiency is suspected